MPs could soon be forced to debate the so-called "Granny Tax" due to come into force this April, as a petition calling for its abolition has attracted almost 100,000 signatures.

After the e-petition was featured in a recent article in The Telegraph, the number of signature jumped from 75,000 to more than 91,000. If a further 9,000 sign this should trigger a parliamentary debate on this issue.

Those signing are protesting against the latest tax grab on pensioners – which is due to raise £3.5bn.

In April the Government plans to abolish the special age-related tax allowances which pensioners have enjoyed since 1925. These currently give pensioners a higher tax allowance than the general public, so they can earn an extra £3,000 from pensions or savings before paying income tax.

However, this allowance does not apply to the richest pensioners, as a clawback facility means that pensioners with an income of £27,000 or more do not benefit from this higher personal allowance.

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Under current plans anyone who reaches their 65th birthday after April 5th this year will now longer qualify for this higher allowance, and it will be frozen for those already in receipt of it – meaning its value will be seriously eroded over time.

Ros Altmann an economist and leading pensions specialist said: "I am not against a simplification of the tax system, but the politicians really need to look at whether this is the fairest way to achieve this." As she points out this change hits middle-income savers hardest. "Those who are reliant solely on their state pension, and who have not saved for their retirement are not going to be affected as they don't get enough income to pay tax. The wealthiest pensioners are similarly unaffected."

But those who have "done the right thing and tried to be self-reliant, often in quite difficult circumstances" now stand to lose out as a result of these changes, she said.

At the same time many of these savers are being squeezed by other areas of policy: with the rates paid on savings plunging, thanks to historically low interest rates and the Government's new Funding for Lending scheme.

Baroness Joan Bakewell, a campaigner for older people called these changes "fundamentally unfair". She said: "The claim that it makes things simpler for pensioners to understand just adds insult to injury."

Neil Duncan-Jordan, a spokesman for the National Pensioners Convention – which has launched this online petition – said: ""We want as many people as possible to sign the petition as we need to get the plight of pensioners higher up the political agenda. We do not object to harmonising the tax regimes of those in work and people who are retired. But it should not be done by penalising pensioners."

The Coalition defended its policy, saying that as the personal allowance for all is rising, it is no longer necessary to make pensioners a special case.

According to the Government, 4.4 million pensioners will lose an average £83 in the 2013-14 tax year. However, many could find themselves paying up to £479 more tax next year, or £511 if they are aged over 75, than they might have expected before this change, costing a couple nearly £1,000.

In the current tax year, for example, the personal allowance for under-65s rose by £630 to £8,105, and is due to leap again to £9,440 in April, with a target of £10,000 during this parliament.

Ms Altmann added: "As recently as 2011, George Osborne said that the age-related allowance would be increase in line with inflation, as measured by the Retail Price Index. Now we find that it has been taken away for some, and frozen for others."